The present invention relates to a color filter which is obtained by coloring a picture element part with an ink jet system and which is suitable for a color liquid crystal display and a process for producing the same.
Recently, there has been a tendency that a demand for a liquid crystal display, particularly a color liquid crystal display is increasing with the development of a personal computer, particularly a portable personal computer. However, since this color liquid crystal display is expensive, a demand for the cost-cut is getting higher and, in particular, a demand for the cost-cut of a color filter weighing in a respect of cost is high.
In such a color filter, a liquid crystal usually operates as a shutter by equipping with three primary colors of red (R), green (G) and blue (B) and switching ON and OFF of an electrode corresponding to each picture element part of R, G and B and the color display is performed by transmission of the light through each picture element part of R, G and B.
As a process for producing a color filter which has hitherto been carried out, there is, for example, a dyeing process. In this dyeing process, a water-soluble polymer material which is a material for dyeing is first formed on a glass substrate, which is patterned into the desired shape by a photolithography step and the resulting pattern is dipped into a dyeing bath to obtain a colored pattern. This is repeated three times to form a color filter layer consisting of picture element parts of R, G and B.
Alternatively, as an another method, there is a pigment dispersing method (color resist method). In this method, a photosensitive resin layer in which a pigment is dispersed is first formed on a substrate and this is subjected to patterning to obtain a monocolor pattern. Further, this step is repeated three times to form a color filter layer consist of picture element parts of R, G and B.
As a still another method, there are an electrode position method and a method of dispersing a pigment in a thermosetting resin and performing three times printing of R, G and B and, thereafter, thermally curing the resin. However, in any method, the same step needs to be repeated three times for coloring three colors of R, G and B, and there is a problem that the cost is high and a yield is decreased because of repetition of a step.
As a process for producing a color filter which has solved these problems, there is proposed a method of blowing a coloring ink with an ink jet system to form a colored layer (picture element part) (JP-A-59-75205). In the publication, there are disclosed a method in which a convex part which is a border is printed in advance with a material having the worse wettability on an ink when an ink having the better wettability on a glass substrate is used, and a method in which a pattern is formed in advance with a material having the better wettability on an ink to help the ink fixation when an ink having the worse wettability on a glass is used. However, there is no description regarding how to specifically coat a material having the better wettability and a material having the worse wettability.
On the other hand, as another process for producing a color filter by blowing a coloring ink by an ink jet system to form a colored layer (picture element part), there is disclosed a method of treating a concave part with an inkphilic treating agent in JP-A-9-203803. In this method, a convex part is formed in advance on a substrate and this convex part is made to be ink-repellent and, thereafter, the whole substrate is surface-treated with the inkphilic treating agent. However, in this method, since a convex part needs to be ink-repellent in advance upon the inkphilic treatment, there is a problem that two times treatments of the ink-repulsion treatment and the inkphilic treatment need to be performed.
In addition, as a method for producing a color filter by forming a colored layer with an ink jet system, there is described a method of forming a colored layer (picture element part) by providing an ink absorbing layer on a substrate and making a difference in the ink absorbability of this absorbing layer between an exposed part and an unexposed part in JP-A-8-230314 and JP-A-8-227012. However, in this method, since a colored layer is formed by forming an absorbing layer and absorbing an ink in this absorbing layer, there is a problem that a difference in the coloration between a central part of an ink dot and a surrounding part of that is present which results in the color nonuniformity. In addition, there is also a problem that this absorbing layer needs the predetermined thickness resulted from its function of absorbing an ink.
On the other hand, in a color filter, a shading part called as a black matrix is generally provided on a boundary portion of a picture element part. The shading part generally formed on the side of color filter. However, in case of using as a liquid crystal panel, there are some cases that the shading part is formed on the side of a substrate opposite to the color filter. When the shading part is formed on the side of a substrate opposite to the color filter, a color filter in which a shading part is not provided, is formed. The above-described problems also occur in the color filter which do not has a shading part.
The present invention was done in view of the above problems and a main object thereof is to provide a color filter which do not have a shading part, in which a part having the better wettability and a part having the worse wettability can be formed on a single layer regarding the wettability of a substrate which becomes problematic upon formation of a picture element part with an ink jet system, and a pattern formed of the part having the better wettability and the part having the worse wettability can be formed in a few steps and, further, an ink absorbing layer is not necessary, and which has the better quality and which can be produced with the low cost, and a process for producing the same.
In order to attain the aforementioned object, the present invention provides a color filter which comprises a transparent substrate, a picture element part in which a plurality of colors are provided in the predetermined pattern with an ink jet system on the transparent substrate, and a wettability-variable layer being capable of varying the wettability which is provided for forming the picture element part.
As described above, the present invention is characterized in that it has a wettability-variable layer in order to form a picture element part. Therefore, by utilizing the change in the wettability of a wettability-variable layer, a picture element part can be formed with the better precision, and a high quality color filter having no problem such as color missing and color nonuniformity can be provided.
In this case, the construction may be such that the wettability-variable layer is provided on the transparent substrate, and the picture element part is provided on the wettability-variable layer. By forming such a construction, a wettability-variable layer of a part on which a picture element part is formed can be made to be an inkphilic region having a small contact angle with a liquid in advance, and the other part of the wettability-variable layer can be made to be an ink-repellent region having a large contact angle with a liquid. By coloring the inkphilic region where the picture element part is formed, with an ink jet system, an ink is adhered to only the inkphilic region having a small contact angle with a liquid. Accordingly, the ink is applied uniformly within the whole surface of the picture element part. Therefore, a color filter having no disadvantage such as color nonuniformity and color missing can be provided.
In the present invention, it is preferable that a space (distance) between the picture element parts is not more than 2 xcexcm. Since a color filter of the present invention does not have a black matrix (shading part), when actually using for a liquid crystal panel, it is necessary to use together with a back light side substrate having a black-matrix. In this case, when a space between picture element parts is wide, it is necessary to have a high precision concerning positioning with the back light side substrate which has a black matrix. If it is not so, a back light penetrates the space between the picture element parts, as a result, the so-called color missing may occur. Accordingly, it is preferable that the space between the picture element parts is as small as possible, concretely, it is preferable that the space between the picture element parts is not more than 2 xcexcm. Further, a colored layer consisting of the picture element parts can obtain surface smoothness if the space between the picture element parts is small like that.
In the present invention, an ink-repellent convex part may be formed on a surface of a wettability-variable layer at a boundary portion of the picture element part. Since an ink-repellent convex part is formed on a boundary portion between the picture element parts forming portions when the picture element part is formed by adhering an ink with an ink jet system, the disadvantages such as mixing of inks during coloring, do not occur, being preferable.
On the other hand, in the present invention, the construction may be such that the picture element part is provided on the transparent substrate, and the wettability-variable layer is provided on a border portion between the picture element parts.
In this case, by making the wettability of a wettability-variable layer on a border part of a picture element part, an ink-repellent region having the larger contact angle with a liquid than that of a part on a transparent substrate, on which a picture element part is to be formed, since it is difficult for an ink to migrate over a border part of a picture element part having ink-repellent properties upon coloring a part on which a picture element part is to be provided (picture element part forming portion) with an ink jet system, a color filter having no disadvantages such as ink mixing and the like can be provided. In addition, by making a wettability-variable layer of a border part of a picture element part an inkphilic region having the small contact angle with a liquid thereafter, covering the whole with a protecting layer can be easily carried out and, thus, a color filter having the high quality can be obtained.
In this case, it is preferable that the wettability on the transparent substrate is less than 10 degrees in terms of the contact angle with a liquid having the surface tension of 40 mN/m. This is because, when an ink is adhered to the picture element part forming portion on the transparent substrate with an ink jet system, the ink for the picture element part is uniformly spread with a picture element part forming portion, the better-quality color filter having no disadvantages such as color nonuniformity and the like can be provided.
In the present invention, it is preferable that the wettability-variable layer is a photocatalyst-containing layer comprising at least a photocatalyst and a binder, and having the wettability which varies so that the contact angle with a liquid is decreased by,irradiation with the energy.
Like this, by forming a photocatalyst-containing layer having the wettability which varies so, that the contact angle with a liquid is decreased by irradiation with the energy, the wettability of this layer can be varied by performing the pattern irradiation of the energy and the like and an inkphilic region having the small contact angle with a liquid can be formed easily and, for example, it becomes possible to easily make only a part on which a picture element part is formed into an inkphilic region. Accordingly, when a shading part is not provided between the picture element parts, the picture element part can be easily formed, and a color filter without a shading port can be manufactured effectively.
In a color filter described above, it is preferable that the photocatalyst-containing layer contains fluorine and the photocatalyst-containing layer is formed so that the content of fluorine on the surface of the photocatalyst-containing layer is decreased by the action of the photocatalyst as compared with before the irradiation of the energy upon irradiating the photocatalyst-containing layer with the energy.
As mentioned above, since a color filter of the present invention is constructed such that the fluorine content of the energy irradiated part on a photocatalyst-containing layer formed on a transparent substrate is decreased, a pattern comprising a part in which the fluorine content is decreased can be formed by the pattern-irradiation of the energy. Since when the fluorine content is decreased, the part becomes a region having the high inkphilicity as compared with other parts, it becomes possible to easily make only a part on which a picture element part and the like is formed an inkphilic region, and a color filter can be easily manufactured.
Further, in a color filter described above, it is preferable that the fluorine content of a part in which the fluorine content is decreased by irradiating the photocatalyst-containing layer with the energy, is 10 or less relative to 100 of the fluorine content of a part which was not irradiated with the energy.
When, like this, the fluorine content of a part having the lower fluorine content which was formed by irradiating the photocatalyst-containing layer with the energy, is 10 or less based on the weight relative to 100 of the fluorine content of a part which is not irradiated with the energy, a great difference in the inkphilicity between a part irradiated with the energy and a part not irradiated with the energy can be produced. Therefore, by forming a picture element part and the like on a photocatalyst-containing layer on which such the pattern is formed, it becomes possible to precisely form a picture element part and the like on only an inkphilic region having the reduced fluorine content and a color filter can be manufactured with the better precision.
The photocatalyst comprised in the photocatalyst-containing layer, is preferably one or more selected from the group consisting of titanium oxide (TiO2), zinc oxide (ZnO), tin oxide (SnO2), strontium titanate (SrTiO3), tungsten oxide (WO3), bismuth oxide (Bi2O3), and iron oxide (Fe2O3). Inter alia, titanium oxide (TiO2) is preferable. This is because since titanium oxide has the high band gap energy, it is effective as a photocatalyst, is chemically stable, has no toxicity and is easily available.
In the case of a color filter in which a photocatalyst is titanium oxide, it is preferable that it has a photocatalyst-containing layer in which fluorine element is contained in the surface of the photocatalyst-containing layer at an amount of 500 or more relative to 100 of titanium element as quantified by a X-ray photoelectron spectroscopic method.
This is because, when such the degree of fluorine (F) element is contained, the ink-repellent properties of a part not irradiated with the energy are sufficient and, when a pattern of a part having the reduced fluorine (F) element content by the energy irradiation is formed and a picture element part and the like are formed thereon, an ink and the like do not drop out into a part other than a part on which a picture element part is formed and a color filter can be manufactured more precisely.
On the other hand, in a color filter described above, a binder which is the other component constituting a photocatalyst-containing layer is preferably organopolysiloxane having a fluoroalkyl group.
The reasons are as follows. In a color filter of the present invention, as a method of inclusion of fluorine element in a photocatalyst-containing layer, mention may be made of various methods. However, by using organopolysiloxane having a fluoroalkyl group as a binder, fluorine element can be easily contained in a photocatalyst-containing layer and the content thereof can be easily reduced by the energy irradiation.
In addition, in a color filter described above, it is preferable that a binder which is the other component constituting a photocatalyst-containing layer, is formed of organopolysiloxane which is one or more of a hydrolyzed condensed compound or a co-hydrolyzed condensed compound of a silicon compound represented by YnSiX(4xe2x88x92n) (wherein Y represents alkyl group, fluoroalkyl group, vinyl group, amino group, phenyl group or epoxy group, X represents alkoxy group or halogen, and n is an integer of 0 to 3).
In a color filter described above, it is preferable that a silicon compound having a fluoroalkyl group among the aforementioned silicon compounds constituting the aforementioned organopolysiloxane is contained at an amount of not less than 0.01 mol %.
The reasons are as follows. When a silicon compound having a fluoroalkyl group is contained at an amount of not less than 0.01 mol %, fluorine element is sufficiently contained in the surface of a photocatalyst-containing layer and it is possible to make larger the difference in the wettability between an inkphilic region on a photocatalyst-containing layer having the reduced fluorine element content resulted from the energy irradiation and an ink-repellent region on the surface of a photocatalyst-containing layer not irradiated with the energy. Accordingly, an ink and the like can be precisely attached into an ink-repellent region without dropping out upon formation of a picture element part and the like on an inkphilic region, and a color filter having the better quality can be manufactured.
In the present invention, it is preferable that the contact angle with a liquid having the surface tension of 40 mN/m on the photocatalyst-containing layer is 10 degrees or more in a part not irradiated with the energy and the angle is less than 10 degrees in a part irradiated with the energy. Since a part not irradiated with the energy is a part requiring the ink-repellent properties, when the contact angle with a liquid having the surface tension of 40 mN/m is less than 10 degrees, the ink-repellent properties are not sufficient and there is a possibility that an ink and a coating material for a shading part and the like remain, being not preferable. On the other hand, when the contact angle of a part irradiated with the energy with a liquid having the surface tension of 40 mN/m is 10 degrees or more, there is a possibility that the spread of an ink and a coating material for a shading part is inferior, color missing and the like may occur in a picture element part.
Further, in the present invention, it is preferable that a picture element part colored with the aforementioned ink jet system is a picture element part colored with an ink jet system using an UV-curing ink. This is because, after a picture element part is colored with an ink jet system by using an-UV curing ink, UV is irradiated and, thereby, an ink can be rapidly cured, which can be sent to a next step, being preferable in a respect of the efficiency.
A liquid crystal panel having the aforementioned color filter and a opposite substrate having a shading part, and which is obtained by encapsulating a liquid crystal compound between both substrates, has the advantages of the aforementioned color filter, that is, the advantages that color missing and color nonuniformity of a picture element part are not present and it is advantageous in a respect of cost.
In order to attain the aforementioned object, the present invention provides a process for production of a color filter, which comprises steps: (1) a step of providing a photocatalyst-containing layer having the wettability of the energy-Irradiated part which changes in a direction of reduction of the contact angle with a liquid, on a transparent substrate, (2) a step of forming an exposed part for a picture element part by pattern-irradiating with the energy on a picture element part forming portion on which the picture element part, on the photocatalyst-containing layer formed on the transparent substrate, is to be formed, and (3) a step of coloring the exposed part for a picture element part with an ink jet system, to form a picture element part.
In a process for producing a color filter in the present invention, by providing a photocatalyst-containing layer on a transparent substrate and irradiating this photocatalyst-containing layer with the energy, an exposed part for a picture element part, on which the contact angle with a liquid of the energy-irradiated part is reduced, can be formed. By coloring the exposed part for a picture element part with an ink jet system, the picture element part can be easily formed. Accordingly, it is possible to form the picture element part with the ink jet system with advantageous in a respect of cost even if there is no shading part on the transparent substrate.
Further, in the present invention, the step of forming an exposed part for a picture element part, then coloring the part with an ink jet system to form the picture element part, may comprise steps; (a) a step of forming a exposed part for a first picture element part by pattern-irradiating with the energy on a part of a picture element part forming portion on which the picture element part, on the photocatalyst-containing layer, is to be formed, (b) a step of forming a first picture element part by coloring the exposed part for a first picture element part with the ink jet system, (c) a step of forming a exposed part for a second picture element part by irradiating with the energy on a remaining part of a picture element part forming portion on which the picture element part, on the photocatalyst-containing layer, is to be formed, and (d) a step of forming a second picture element part by coloring the exposed part for a second picture element part with the ink jet system.
When a picture element part is formed on a transparent substrate without a shading part, it is not possible to use the shading part as a partition during coloring a picture element part. Therefore, in case of forming a picture element part through coloring a exposed part for a picture element part converted to inkphilic region by irradiating with the energy, and when a space between the exposed parts for a picture element part is narrow, that is, when a width of an ink-repellent region not exposed is narrow, there are some possibilities of mixing some sorts of ink for adjacent picture element parts through migration over an ink-repellent region during forming a picture element part. Accordingly, it is desirable to form adjacent picture element parts as apart as possible during formation of the picture element part. As described above, when the method such that the second picture element part is formed after the first picture element part is formed, is employed, the adjacent picture element parts can be formed on apart positions each other during formation of the first picture element part because the energy can be pattern-irradiated such that the picture element part is formed alternately during formation of the first picture element part. Since the exposed part for a first picture element part is formed the condition such that relatively wide ink-repellent region exist between the colored regions, like that, and is colored with an ink jet system, there is no possibility of mixing some sorts of ink for adjacent picture element parts. Then, the exposed part for a second picture element part is formed though exposing again between the first picture element parts formed like that, and then is colored with the ink jet system, as a result a color filter which do not have deficiency such as ink mixing, can be obtained. Further, concerning a color filter which do not have a shading part, there are some demands such that no space exist between picture element parts. In this case, it is necessary to employ the method such that the formation of picture element parts divides into two times, described above.
In the present invention, an exposed part for an ink-repellent convex part where an ink-repellent convex part is to be formed, may be formed before formation of the exposed part for a picture element part, and then an ink-repellent convex part may be formed on the exposed part for an ink-repellent convex part through using resin composition. By forming an ink-repellent convex part like this, for example, when the ink-repellent convex part is formed around the region where a picture element part is to be formed, it is possible to prevent the problem such that a picture element part can not be formed precisely because ink flows out at the portion around a color filter. In this invention, particularly, it is preferable to form the ink-repellent convex part between the picture element parts. It is the reason to do so that the above mentioned problem, that is, mixing some sorts of ink for adjacent picture element parts, become hardly to occur.
Further, the present invention provides a process for production of a color filter, which comprises steps: (1) a step of providing a photocatalyst-containing layer having the wettability of the energy-irradiated part which changes in a direction of reduction of the contact angle with a liquid, at a boundary portion of a picture element part forming portion on which the picture element part is to be formed, on a transparent substrate, (2) a step of forming the picture element part on the picture element part forming portion on the transparent substrate.
According to this method, first, a photocatalyst-containing layer is provided at the boundary portion of the picture element part on the transparent substrate. When the material which has larger contact angle with a liquid before irradiating the energy than that of a surface of the transparent substrate, is employed to the photocatalyst-containing layer, the picture element part forming portion is an inkphilic region which has smaller contact angle with a liquid than that of the boundary portion on which the photocatalyst-containing layer is formed. Accordingly, the boundary portion of the picture element part forming portion acts as an ink-repellent region. Thus, when ink is adhered to the picture element part forming portion which is an inkphilic region, with an ink jet system in the next step, the adhered ink does not migrate beyond the boundary portion which acts as an ink-repellent region. Hence, it is difficult to generate the problem such as ink mixing during formation of a color filter.
Further, in this case, it is preferable that the wettability on the transparent substrate is less than 10 degrees as a contact angle with a liquid having the surface tension of 40 mN/m. Since the wettability of the surface of the transparent substrate is inkphilic, an ink is uniformly and evenly spread when an ink is adhered on a transparent substrate with an ink jet system. Thus, color missing and color nonuniformity do not generate, and a color filter having the high quality can be obtained.